1. Field of the Invention
This invention relates to reading a plurality of identification tags or labels in a container or space without separately passing each tag through a read station. This invention has particularly useful application in conjunction with cash registers and cash recorders, particularly those which determine the price by scanning or in some way interrogating a coded label on products such as consumer goods and which maintain inventory records. This invention also relates to reading such information using invisible radiant energy in the form of a radio transponder that is realized with integrated circuits fabricated on a monolithic semiconductor chip.
2. Prior Art
It is known in the art of food, clothing, and consumer goods distribution to provide a point of sale or checkout station near the exit of a store in order to allow the identification tags or labels on each of the items of merchandise selected by customers to be read, prices tallied, payment made and inventory counts adjusted. At such checkout stations, each item must be individually removed from a shopping cart or basket and moved past a reader in order to read the stock keeping unit information in the form of the universal product code (UPC) from the label.
U.S. Pat. No. 4,862,160 teaches an inventory data acquisition system where each item of inventory has a tag containing a small passive resonate transponder in the form of a printed circuit. A computerized transceiver mounted on a wheeled cart is moved through the aisles, and the transceiver generates signals causing tags which resonate at a unique pair of frequencies to re-radiate simultaneously a third frequency to which the receiver portion of the transceiver on the cart is tuned. The amplitude of the third frequency detected by the receiver portion is a function of distance and the number of tagged products present on the shelf or rack. With the system of this reference, the accuracy of the number of items is thereby compromised by distance and antenna pattern. Furthermore, the transceiver will have to generate all possible combinations of frequencies in order to interrogate all possible items of inventory such as would be required when the inventory is removed from the shelf by a customer and placed in a shopping basket. Unlike inventory data collection, the items in a shopping basket cannot be predicted at a point of sale.
Because a large retail enterprise may have millions of different items for sale with millions of different stock keeping units, it is not practical to serially interrogate each possible stock keeping unit to determine whether it is present.
U.S. Pat. No. 3,832,530 relates to apparatus for identifying articles such as a suitcase or a mailbag. The objects are moved one at a time through an electromagnetic field. Circuits on the label are powered by the electromagnetic field to change the states of a chain of flip flops on the label in a predetermined fashion thereby absorbing electromagnetic energy in a predetermined pattern. The pattern of electromagnetic energy absorption is sensed and then decoded. The chain of flip flops may be set for different codes. The teachings of this reference do not handle multiple items to be sensed in the read region at the same time and do not allow one or more of a plurality of items to be individually addressed and requested to store data. Further, this prior art technique requires a magnetic shielded box which is expensive and inconvenient.
U.S. Pat. No. 4,471,345 describes a tag and portal system for monitoring the whereabouts of, for example, people wearing the tags. Up to six tags may be simultaneously interrogated as their holders pass through a doorway. The tags respond to interrogation signals generated by the portal and their response occurs after a pseudorandom delay. The pseudorandom delay is used to avoid data collisions by the six responding tags.